1. Field of the Invention:
The invention relates generally to floating cutterbar type headers and more particularly to such a header with an automatic header height control system.
2. Prior Art:
Several examples of automatic header height control systems for floating cutterbar type headers are shown in U.S. Pat. Nos. 3,886,718 Talbot, 3,698,164 Boone, 3,597,907 Neal, and 2,913,865 Carruthers. The Talbot and Boone patents include feeler members 55 and 36 respectively movable in response to shifting of the cutterbar relative to the header. Each patent shows an electrical system for transmitting raise or lower signals from the feelers to the control valve of the header lift system. The Neal patent senses pressure changes in the header lift system and transmits electrical signals to a control valve for raising and lowering the header. The Carruthers patent shows a mechanical system from a cutterbar for shifting a control valve between raise and lower positions to thus move the header. The systems having electrical components raise considerations of ease of field service and adjustment. Moreover, all the illustrated systems appear to move the header up or down at fixed rates--a sort of "on-off" response to sensing ground level variations. While variable rate systems are known in the art (assignee's combine Models 815 and 915), none are known to exist in a floating cutterbar type header wherein feelers or the like have been eliminated.
Practical considerations for automatic header height control systems are reliability in operation and maintaining the cutterbar in cose cutting relation to the ground to minimize gathering losses while concurrently preventing damage to the cutterbar and header.